Burner with ultrasonic vibrator

ABSTRACT

A burner with an ultrasonic vibrator of the type for atomizing liquid fuel for combustion is improved as follows: (1) an outer and inner diffusers which are separated from each other by an inner duct are disposed so as to surreound the fuel atomizing surface, that is the front end of a hollow horn; (2) the front end of the inner diffuser is made coincident with the front end of the outer diffuser or located rearwardly of the front end of the outer diffuser whereas the front end of the hollow horn is made coincident with or located intermediate between the front ends of the inner and outer diffusers, (3) the length L of the inner diffuser and the distance l between the rear ends of the inner duct and of the inner diffuser satisfies the following relation:

United States Patent [191 Hori et a1.

[451 Dec. 3, 1974 1 BURNER WITH ULTRASONIC VIBRATOR [75] Inventors: Makoto Hori, Nara; Nerumitsu Rokudo; Toshiyuki Ishiguro, both of Yamatokoriyama, all of Japan [73] Assignee: Matsushita Electric Industrial Co., Ltd, Kadoma-shi, Osaka-fu, Japan [22] Filed: June 26, 1973 [21] Appl. No.: 373,685

Primary ExaminerM. Henson Wood, Jr. Assistant Examiner-John J. Love [57] ABSTRACT A burner with an ultrasonic vibrator of the type for atomizing liquid fuel for combustion is improved as follows: (1) an outer and inner diffusers which are separated from each other by an inner duct are disposed so as to surreound the fuel atomizing surface, that is the front end of a hollow horn; (2) the front end of the inner diffuser is made coincident with the front end of the outer diffuser or'located rearwardly of the front end of the outer diffuser whereas the front end of the hollow horn is made coincident with or located intermediate between the front ends of the inner and outer diffusers, (3) the length L of the inner diffuser and the distance I between the rear ends 'of the inner duct and of the inner diffuser satisfies the following relation:

(4) the hollow horn, and the inner and outer diffusers satisfy the following relations:

D/S 7 to 12 P/D 3 to 6, and

P/S 35 to 60 where (5) the outer duct has a tapered section formed between a large-diameter rear section and a smalldiameter front section thereof, the taper of thetapered section resembling that of the hollow horn.

9 Claims, 13 Drawing Figures Q it IGNITION OIL FLOW TRANSFORMER CONTROL fro UNIT 18 otmsone l i WAVE GENERATOR PA'I'ENIELDEB 3W 3.851.823

SHEEI 16? 5 IGWNITION f TRANSFORMER ULTRASONIC WAVE GENERATOR mamm l: 31m 3,851,823

- SIIEEI' u [If 5 FIG. 5A

INSTABLE INCOMPLETE COMB STION COMBUSTION TABLE COMBUSTION CONDITION I CO2I%) OO- moo o poaooory mammao III SMOKE NO.

BACKGROUND OF THE INVENTION The present invention relates to a burner with an ultrasonic vibrator.

In the burners of the type for atomizing liquid fuel, the velocity transmitted to finely divided liquid fuel particles is considerably smaller than the velocity transmitted to the finely divided fuel particles in the fuel injection type burners so that the flow of atomized fuel particles is easily affected by the air flow. Therefore, a special arrangement must be provided for suitably mixing the atomized fuel particles with air for optimum combustion. More particularly, the sufficient kinetic energy must be-transmitted to the finely divided fuel particles so as to be mixed with air, and therelative positions and dimensions of an inner and outer diffusers which are provided in order to facilitate the optimum mixing of finely divided particles with air must be so determined as to ensure the complete combustion. Otherwise, the turbulent flame front is generated and the flame fluctuates, thus resulting in the vibrations of the burner and hence the increase in noise, and blow-off.

In the conventional burners, the air discharged into the burner strikes against some obstacles so that the turbulent air flow enters into a diffuser. As a result, the uniform mixing of finely divided fuel particles with air cannot be attained, resulting in the incomplete combustion.

SUMMARY OF THE INVENTION Briefly stated, according to the present invention, an inner duct is disposed coaxially of a frustoconical hollow horn. so as to surround it. Primary air isdischarged through the passage between the outer duct. and the hollow born to be mixed with liquid particles atomized at the front end of the hollow horn whichin turn is coupled to an ultrasonic vibrator. Atomizedfuel particles are carried away from the front end or atomizing surface of the hollow horn by air discharged through the outer duct, mixed with air and burnt. The combustion efficiency is depend upon the quantity of primary air supplied, the velocity distribution and the turbulence of the primary air, and the air-fuel ratio.

Inner and outer diffusers each comprising a plurality of blades aredisposed coaxially of the hollow horn so as to surround its fuel atomizing surface, that is the front end thereof, in spaced apart relation. The inner and'outer diffusers are separated from each other by an inner duct in the form of a cylinder which makes complete contact with.the outer peripheral surface of the air-fuel mixture may be suitably controlled. The hollow horn and the inner diffuser are so arranged that their front ends will not extend beyond the front ends of the outer diffuser and of the inner duct. In order to attain an optimum combustion, the rear end of the inner duct is extended beyond the rear end of the inner diffuser, and the distance between the rear ends of the inner duct and of the inner diffuser must be within a predetermined range. In order to steamline the air flowing into the inner and outer diffusers and the annulus between the inner duct and the inner diffuser, the outer duct is provided with a tapered section formed between the large-diameter rear section and the reduced diameter front section, the taper of the tapered section resembling that'of the frustoconical hollow horn. Furthermore, the ratios among the areas of an annulus defined between the inner duct and diffuser and openings at the front ends of the inner and outer diffusers through all of which are discharged air flows are suitably selected. I

The above and other objects, features and advantages of the present invention'wll become more apparent from the following description of one preferred embodiment thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING:

= FIG. 1A is a longitudinal sectional view of a burner in accordance with the present invention;

FIG. 1B is a front end view thereof; FIG. 2 is a fragmentary view, of an enlarged scale of the burner shown in FIG. 1A; I

FIGS. 3A, 3B and 3C are views used for the explanation of the flame front obtained when the position of the front end of the inner duct with respect to the front end of a frustoconical hollow horn is varied;

FIGS. 4A, 4B, 4C and 4D are views used for the explanation of the flame front obtained when the ratios among three air discharge openings are varied; and

FIGS. 5A, 5B and 5C illustrate data obtained by the experimentswhen the ratios among the three air discharge openings are varied as shown in FIGS. 4A to 4D.

DESCRIPTION 0F THE PREFERRED EMBODIMENT:

and is supported within the outer duct 2 by means of a plurality of brackets 15 which are fixed to the hollow I horn 5 atsuch points which correspond to the node of vibration of the horn, that is at which the hollow horn 5 does not vibrate itself at all. An inner duct 3 disposed within the outer duct 2 adjacent to its open end defines an outer diffuser 6 and an inner diffuser 7, both of which are provided with a plurality of blades as best shown in FIG. 1 (B). An ignition plug 8 is extended through the outer duct 2 and is bent at a right angle at the opened end of thereof so thatits center electrode 11 is located upwardly of and adjacent to the top of the frustoconical hollow horn 5. The ignition plug 8 is com nected through a cable 12 to an ignition transformer 13. An oscillator 18 is coupled through a conductor 17 to the vibrator 4. An oil flow control unit 10 is connected to an oil supply pipe 9 which extends through the hollow horn 5 at the node 16 thereof and communicates with an oil passage 14 formed in the hollow horn 5 along the axis thereof as best shown in FIG. 1A.

Fuel flows through the pipe 9 and the passage 14 to the atomizing surface, that is the top of the hollow horn, and forms a thin film over the atomizing surface due to the surface tension thin fuel. This thin fuel film is immediately broken and atomized due to the ultrasonic vibrations of the hollow horn 5. Both the particle size and kinetic energy of the atomized or finely divided particles are very small, and the distribution of the atomized fuel particles is not regular and the concentration of the atomized fuel particles is considerably high in the ignition zone. In order to secure the stable ignition zone to ensure the complete combustion by mixing the atomized fuel particles with air, the outer and inner diffusers 6 and 7 are disposed in order to provide a circumferential discharge of air. That is, the atomized fuel particles are carried out of the atomizing surface of the hollow horn 5 by the air flow discharged through the outer duct and then discharged circumferentially by the inner and outer diffusers 6 and. 7 so that the atomized fuel particles are mixed with air. If the inner duct 3 were not provided, the radial component of the discharged air would separate or shear a body of atomized fuel particles and the atomized fuel particles of relatively larger size. would be transmitted with the sufficient energy to leave from the mixing zone. As a result, incomplete combustion would occur, and the mixture of atomized fuel particles with air in the ignition zone would be adversely affected, resulting in the blow-off" and combustion noise. To overcome this problem, according to the present invention, the positions of the hollow born 5, the outer and inner diffusers 6 and 7 with respect to each other, the positions and length of the blades of the inner and outer diffusers 7 and 6, and the opening or passage areas of the inner and outer diffusers 7 and 6 are limited. As shown in FIG. 2, assume that the distance between the front end of the inner duct 3 and the front end of the inner diffuser blade 7 be M; and the distance between the front end of the hollow horn 5 and the front end of the inner duct 3 be m. Then, the experiments conducted by the inventors show that when m 0. that is when the front the hollow horn 5 by a relatively long distance so that the air flow strikes the leading end of the flame front. Therefore, the flame is distrubed at its leading end and fluctuates in response to even a small pressure variation in the furnace, thus resulting in the great combustion noise. Furthermore, a part of the flame is displaced out of the mixing zone, thus resulting in the incomplete combustion. When the draft is too strong, the flame is blown off.

When the front end of the hollow horn S is located backwardly of the front ends of the inner duct and of the inner diffuser blade 7, that is when M m, the circumferential discharge of the air at the atomizing surface of the hollow born is enhanced as shown in FIG. 30 and the negative pressure is produced in the area adjacent to the fuel atomizing surface of the hollow horn 5 so that the flame is drawn back to the atom izing surface. The fuel atomizing surface becomes the flame generating or starting position, and a part of the flame strikes back into the inner diffuser, thus resulting in the incomplete combustion. Soot would be deposited upon the fuel atomizing surface of the hollow horn 5 and the blades 7 of the inner diffuser so that they are overheated and oxidized, resulting in a shorter service life. Furthermore, the back fire tends to occur very often due to the back flowing from the chimney.

When O 5 m i M, the flame front starts from the position slightly spaced apart from the fuel atomizing surface of the hollow horn 5 as shown in FIG. 3b so that the defects encountered in the arrangements shown in FIGS. 3A and 3C may be overcome.

The air flowing through the casing l strikes against the base or rear end of the hollow horn 5 so that the disturbance or turbulence occurs. If the turbulent air is introduced into the inner and outer diffusers 6 and 7, the circumferential flow will be also disturbed so that the atomized fuel particles will not be uniformly mixed with air, thus resulting in the incomplete combustion, the turbulent flame and the abnormal combustion noise. To overcome this problem, the inner and outer diffusers 6 and 7 are separated by the inner duct 3 whose rear end is spaced apart rearwardly of and from the inner and outer diffusers 7 and 6. Furthermore the tapered section 2a of the outer duct 2 has the same taper as that of the hollow horn 5 so that the air flow may be streamlined before it enters into the inner and outer diffusers. Assume that the length of the inner diffuser 7 be L and the distance between the rear ends of the inner duct 3 and of the inner diffuser 7 be I. When the distance I is so small that L/8 l L/4, the air flow which strikes against the rear end of the inner duct 3 and is disturbed flows into the outer and inner diffusers. Therefore, it becomes difficult to control a suitable ratio between the quantities of air entering into the outer and inner diffusers 6 and 7. As a result, incomplete combustion occurs.

When the distance I is long such as L/2 I, the rear end of the inner duct 3 approaches the rear end of the hollow horn 5 at which the turbulent air flow is most prominent. Therefore, the turbulent air enters into the outer and inner diffusers 6 and 7 so that the air discharged therefrom is also disturbed, thus resulting in incomplete combustion.

Therefore, the position of the rear end of the inner duct 3 must be determined in such a manner that the air flow disturbed at the rear end of the hollow horn 5 may be sufficiently streamlined in the passage defined by the tapered section 2a of the outer duct 2 and the hollow horn 5 before it reaches the rear end of the inner duct 3 and that the air flow disturbed at the rear end of the inner duct 3 may also sufficiently streamlined before it enters into the outer and inner difiusers 6 and 7. The extensive experiments conducted by the inventors show that the distance I must be L/4 l U2. The burner which satisfies the above described conditions has the following features:

1. The flame front is stabilized because the circumferential air flow is not disturbed.

2. The fluctuation of the flame is eliminated so that the combustion noise may be reduced.

3. An optimum air-fuel ratio may be obtained in the air-fuel mixing zone so that complete combustion may be ensured. In order to attain the above advantages, an optimum ratio of the quantity of air passing through the inner diffuser to that of the air passing through the outer diffuser must be determined.

Assume that the area of an annulus between the front end or fuel atomizing surface of the hollow horn 5 and the inner diffuser 7 (which will be referred to as the first air passage area hereinafter) be S and the area of the air passage of the inner diffuser 7 (which will be referred to as the second air passage area" hereinafter) be D and the area of the air passage of the outer diffuser 6 (which will be referred to as the third air passage area" hereinafter) be P.

The air flow passing through the first air passage S streamlines the atomized fuel particles and carries them forwardly of the fuel atomizing surface of the hollow cone 5. The air flow passing through the second air passage D is a circumferential discharge which serves to form the fuel-air mixing zone and the ignition zone which in turn maintain the undisturbed flame. The air flow passing through the third air passage P is also a circumferential discharge which serves to keep the flame in the ignition zone undisturbed and determines the configuration of the flame as well as the air-fuel ratio.

When the ratio of the second air passage area D to the first air passage area S is large, the air pressure drops at the front end of the hollow horn 5, and the negative pressure is produced by the air flow passing through the second air passage D. As a result, the flame front starting position approaches the inner cicumference of the inner diffuser 7 as shown by the chain lines a in FIG. 4A. Soot is deposited upon the inner diffuser blades so that the first air passage area S is reduced and the above described adverse effect is further increased.

When the ratio D/S is small, the pressure of the air passing through the first air passage S'rises too high so that the flame starting position is spaced apart from the front end of the hollow horn 5 as indicated by the twodot chain lines 17 in FIGJllA. The ignition is adversely affected and the flame fluctuates, thus resulting in an increase in combustion noise.

When the ratio D/S is large, the length of the flame becomes shorter and is diverged so that the atomized fuel particles which have not been burnt yet escape from the air-fuel mixing zone, thus resulting in a decrease in combustion efflciency. When D/S is smaller, the flame front extendsin the form of a cylinder and becomes longer.

When the ratio P/D of the third air passage area to the second air passage area D is large, the negative pressure is produced substantially all over the front end of the outer diffuser 6 as indicated by the chain lines c in FIG. 48 so that the flame makes contact with the substantial area of the outer and inner diffusers 6 and 7. Soot is deposited upon the outer and inner diffusers. The flame becomes large in cross sectional area but becomes shorter, and the volume of air in the flame is not sufficient to ensure the complete combustion. When P/D is small, the pressure is extremely increased adjacent to the front end of the hollow horn 5 as indicated by the two-dot chain lines d in FIG. B so that the flame front starting position is spaced apart from the front end of the hollow horn 5 by a relatively greater distance; As a result, the flame is disturbed, and blowof occurs.

When the ratio P/S of the third air passage area P to the first air passage area S is large, the frame front is as indicated by the chain lines e in FIG. dC and is substantially similar to the flame front indicated by the chain lines 0 in FIG. 413 so that the similar adverse effects are produced. When the ratio P/S is small, the flame front is as indicated by the two-dot chain lines f in FIG. 4C

and is intermediate between the flame fronts indicated I by the lines in FIG. 4C and lines b in FIG. 4A.

The above described adverse effects are produced under the following conditions:

Therefore, it follows that the optimum combustion can be obtained under the following conditions:

7 D/S l2,3 P/D 6and35 P/S 60. FIG. 4D illustrates the flame front obtained under the above conditions (lines 3) and when the air distribution is optimum. In this case, the following conditions are observed: i

l. The body of atomized fuel particles is streamlined by the air flow flowing through the first air. passage S and the flame front starts very close to the front end of the hollow born 5. The ignition is positive and the flame is stabilized. The flame does not fluc-' and substantially complete combustion can beattained.

3. The air flow discharged through the third air passage encircles the' combustion zone formed by the air flows discharged through the first and second airpassages, and serves to mix unburnt fuel particles with air, thereby ensuringthe complete combustion.

' Experimental data obtained when the air passage ratiosD/S, P/D and P/S were varied over a relatively wide a 'range are illustrated in FIGS. 5A 5C. As shown in FIG.- 5A, when the ratio D/S is large, a substantial quantity of fuel is left unburnt, that is, incomplete combustion occurs. The best result is obtained when the ratio D/S is within the range between 7 and 12. In like manner, the best result is obtained when the ratio P/D 3 to 6 and when the ratio P/S 35 to as shown in FIGS. 53 and 5C.

For example, when D/S 8, P/D 5 and P/S 40, carbon dioxide was 9 10 percent, carbon monoxide was 0.005 0.01 percent, and-smoke number isl. When D/S 12, P/D 3 and P/S 36, carbon dioxide was 9 10.5 percent, carbon monoxide 0 0.005 perc. means for supplying liquid fuel to a fuel portopened at the front end of said hollow horn,

d. an inner diffuser disposed coaxially of said hollow horn so as to surround the leading portion thereof in spaced apart relation,

e. an outer diffuser disposed coaxially and outwardly of said inner diffuser,

f. an inner duct separating said inner diffuser from said outer diffuser,

g. the front end of said inner diffuser being within the front ends of said outer diffuser and of said hollow hone,

h. the front end of said hollow horn being within the front end of said outer diffuser and i. said inner duct surrounding both the outer periphery of said inner diffuser and the inner periphery of said outer diffuser.

2. A burner as defined in claim 1 wherein the rear end of said inner duct is extended beyond the rear end of said inner diffuser; and the following condition is satisfied:

where L axial length of said inner diffuser and I distance between the rear ends of said inner diffuser and of said inner duct. 3. A burner as defined in claim 1 wherein said outer duct has a tapered section formed between a large diameter rear section and a small diameter front section 4. A burner as defined in claim I wherein said inner duct and said inner diffuser are located with respect to each other so as to satisfy the following condition:

where M distance between the front ends of said inner duct and of said inner diffuser, and m' distance between the front ends of said inner duct and of said hollow horn. 5. A burner as defined in claim 1 wherein said hollow horn, and said inner and outer diffusers satisfy the following conditions:

' D/S 7 to 12 P/D 3 to 6, and W8 35 to 60 where S area of an annulus between said front end of said hollow horn and said inner diffuser through which air is discharged;

D area of an opening at the front end of said inner diffuser through which is discharged air; and

P area of an opening at the front end of said outer diffuser through which is discharged air.

6. A burner as defined in claim 1 wherein a. the rear end of said inner diffuser is extended beyond the rear end of said inner diffuser; and the following condition is satisfied:

where L axial length of said inner diffuser, and I distance between the rear ends of said inner dif fuser and of said inner duct;

b. said inner duct and said inner diffuser are located with respect to each other so as to satisfy the following condition:

0 g m g M where M distance between the front ends of said inner duct and of said inner diffuser, and m distance between the front ends of said inner duct and of said hollow hone;

c. said hollow horn, and said inner and outer diffusers satisfy the following conditions:

D/S 7 to l2 P/D 3 to 6, and

P/S 35 to 60 where S area of an annulus between said front end of said hollow horn and said inner diffuser through which is discharged air,

D X area of an opening at the front end of said inner diffuser through which is discharged air, and

P area of an opening at the front end of said outer Om M where M distance between the front ends of said inner duct and of said inner diffuser, and m distance between the front ends of said inner duct and of said hollow born 8. A burner as defined in claim 5 wherein said outer duct has a tapered section formed between a large diameter rear section and a small diameter front section so as to surround a part of said hollow horn 9. A burner as defined in claim 6 wherein said outer duct has a tapered section formed between a large diameter rear section and a small diameter front section so as to surround a part of said hollow horn.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 1,823 Dated December 3, 1974 Inventofls) MAKO'IO HORI, E I' AL.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 65, "frame" should read flame Column 8, line 28, change "X" to Signed and sealed this 22nd day cf April 1975.

FORM PC4050 (10-59) USCOMlM-DC aoa'lo pu i U BOVIINIIIT FI IYIUG OFFICE I... 0-80-18! 

1. A burner with an ultrasonic vibrator comprising a. a casing and an outer duct fixed to said casing, b. a frustoconical hollow horn for atomizing liquid fuel disposed within said outer duct coaxially thereof and coupled to an ultrasonic vibrator, c. means for supplying liquid fuel to a fuel port opened at the front end of said hollow horn, d. an inner diffuser disposed coaxially of said hollow horn so as to surround the leading portion thereof in spaced apart relation, e. an outer diffuser disposed coaxially and outwardly of said inner diffuser, f. an inner duct separating said inner diffuser from said outer diffuser, g. the front end of said inner diffuser being within the front ends of said outer diffuser and of said hollow hone, h. the front end of said hollow horn being within the front end of said outer diffuser, and i. said inner duct surrounding both the outer periphery of said inner diffuser and the inner periphery of said outer diffuser.
 2. A burner as defined in claim 1 wherein the rear end of said inner duct is extended beyond the rear end of said inner diffuser; and the following condition is satisfied: L/4 < l < L/2 where L axial length of said inner diffuser, and l distance between the rear ends of said inner diffuser and of said inner duct.
 3. A burner as defined in claim 1 wherein said outer duct has a tapered section formed between a large diameter rear section and a smalL diameter front section.
 4. A burner as defined in claim 1 wherein said inner duct and said inner diffuser are located with respect to each other so as to satisfy the following condition: 0 < or = m < or = M where M distance between the front ends of said inner duct and of said inner diffuser, and m distance between the front ends of said inner duct and of said hollow horn.
 5. A burner as defined in claim 1 wherein said hollow horn, and said inner and outer diffusers satisfy the following conditions: D/S 7 to 12 P/D 3 to 6, and P/S 35 to 60 where S area of an annulus between said front end of said hollow horn and said inner diffuser through which air is discharged; D area of an opening at the front end of said inner diffuser through which is discharged air; and P area of an opening at the front end of said outer diffuser through which is discharged air.
 6. A burner as defined in claim 1 wherein a. the rear end of said inner diffuser is extended beyond the rear end of said inner diffuser; and the following condition is satisfied: L/4 < l < L/2 where L axial length of said inner diffuser, and l distance between the rear ends of said inner diffuser and of said inner duct; b. said inner duct and said inner diffuser are located with respect to each other so as to satisfy the following condition: 0 < or = m < or = M where M distance between the front ends of said inner duct and of said inner diffuser, and m distance between the front ends of said inner duct and of said hollow hone; c. said hollow horn, and said inner and outer diffusers satisfy the following conditions: D/S 7 to 12 P/D 3 to 6, and P/S 35 to 60 where S area of an annulus between said front end of said hollow horn and said inner diffuser through which is discharged air, D X area of an opening at the front end of said inner diffuser through which is discharged air, and P area of an opening at the front end of said outer diffuser through which is discharged air.
 7. A burner as defined in claim 2 wherein said inner duct and said inner diffuser are located with respect with each other so as to satisfy the following relation: 0 < or = m < or = M where M distance between the front ends of said inner duct and of said inner diffuser, and m distance between the front ends of said inner duct and of said hollow horn.
 8. A burner as defined in claim 5 wherein said outer duct has a tapered section formed between a large diameter rear section and a small diameter front section so as to surround a part of said hollow horn.
 9. A burner as defined in claim 6 wherein said outer duct has a tapered section formed between a large diameter rear section and a small diameter front section so as to surround a part of said hollow horn. 